1. Field of the Invention
The present invention relates to a measuring unit, a partition member, a mold for molding the partition member, and a production method for the partition member.
2. Description of the Related Art
The following is known as the prior art related to the present invention.
Japanese Unexamined Patent Publication No. Hei 9-304265 (1997), for example, discloses a pellet for use in a particle detector to be incorporated in a particle counter of an electrical resistance type which is adapted to determine the number of particles in a particle suspension passing through a minute through-hole on the basis of a change in electrical characteristic occurring due to a difference in electrical impedance between the suspension and the particles. The pellet is produced by forming one or more minute through-holes in an electrically insulative plastic sheet or film by an excimer laser abrasion method, and has a predetermined shape around each of the minute through-holes.
Japanese Unexamined Patent Publication No. Hei 11-281564 (1999), for example, discloses a unitary pellet which comprises an orifice provided in a center portion thereof, conical slant portions provided on opposite sides of the orifice coaxially with the orifice, and one or more reinforcement members provided between rear surfaces of the slant portions.
An electrical resistance method is known as a method for electrically detecting the number and volume of particles suspended in an electrically conductive liquid. In the electrical resistance method, a channel for the particle suspension is divided by a partition member (pellet) having a minute through-hole, and a change in electrical resistance occurring when the particles pass through the through-hole is detected.
The resistance change ΔR and the volume Vp of the particles have the following relationship:ΔR=(ρo/S2)Vp  (1)wherein ρo is the electrical resistance of the liquid, and S is the cross sectional area of the minute through-hole. For accurate determination of the volume Vp of the particles on the basis of the expression (1), it is necessary to form the minute-hole in the partition member with higher levels of dimensional accuracy and reproducibility.
Therefore, it is a conventional practice to employ artificial ruby or sapphire for the production of the partition member and achieve the formation of the minute through-hole by a laser machining process. However, the artificial ruby and sapphire are hard and, hence, not easy to machine.
Therefore, a partition member produced by employing a more easy-to-machine and softer material than the aforesaid hard material and a partition member reinforced by additionally providing a structural component are under consideration. However, these partition members are insufficient in performance and, hence, make it difficult to provide satisfactory measurement results when employed for the measurement by the electrical resistance method.